1. Field of the Invention
This invention relates to a filter system and specifically to a system utilizing solid and liquid reagents.
2. Description of Related Art
It is conventionally known to use activated charcoal and other materials as adsorptive elements to remove impurities from an airstream. With the advent of effective fiber cross sections, it is possible to produce fibers which are partially hollow. A particularly effective cross sections is one having three T-shaped lobes extending from a central core, as described in U.S. Pat. No. 5,057,368, which is incorporated herein by reference. Conventional filters have used filtering media coated with solid or liquid materials in a variety of applications; however, many of these applications have relied on absorption, rather than adsorption. Adsorption occurs where particles to be removed attach to the surface of the filter materials elements; whereas, absorption occurs where molecular motion mobility is harnessed to move unwanted particles from one zone to another in a non-mechanical manner. The multilobal fiber has been particularly effective as a wicking fiber where certain contaminant-removing liquids or solids are filled in cavities formed within the fiber.
The multilobal fiber filled with solid filtering particles have been used in adsorptive air filtration and odor-removing applications. Such filtering particles have included the use of carbon particles, zeolites, baking soda, cyclodextrins, and solids which could adsorb certain contaminants (see U.S. Pat. No. 5,759,394, which is incorporated herein by reference). Other applications utilizing multilobal-type fibers as wicking fibers also have involved absorptive properties of certain liquids which are filled within the cavities of the fibers. These liquids were typically chosen to lightly absorb odor and gas molecules in a reversible manner from a contaminated airstream to aid in the eventual dispersion of these molecules into a second airstream (see U.S. Pat. Nos. 5,891,221. and 5,704,966, which are incorporated herein by reference).
Maintaining environments free of contaminants is particularly critical in the manufacturing of integrated circuits because wafers are very susceptible to small particles and low levels of certain chemicals. This can be done by manufacturing wafers inside cleanrooms with filtered air. The filters are used to reduce particle and chemical levels to extremely low levels (less than 1 part-per-billion). Semiconductor tools are also sometimes equipped with environmental controls that provide local ultra clean airflow during processing. However, conventional chemical filters have a very short life span, require frequent replacement, and are ineffective at efficiently filtering out certain chemicals.
In accordance with the invention, an ultra-high efficient multilobal fiber filter is described with long life use for chemical contaminant filtering applications. The unexpected ultra efficiency of the fiber filter reduces contaminants to low levels in the parts-per-billion. A reactive reagent, preferably an acid or base and in either liquid or solid form, is disposed within longitudinal slots in each length of fiber. The reagent may be reactive with base contaminants by any known mechanism, such as an acid-base reaction to form ionic bonds, an oxidation-reduction reaction, and various other organic and inorganic reaction mechanisms as known in the art to form covalent bonds, hydrogen bonds, coordination compounds, or complex compounds. The reagent may be used alone or in conjunction with solid adsorptive particles which may also be utilized with the reagents in the longitudinal slots within the fibers. The fibers are formed into a single layered, in one embodiment, or a multi-layered fiber mat, in another embodiment, but the reagents remain exposed to the flow of a contaminated airstream passing through the filter. The contaminants in a fluid stream react within the longitudinal slots of the fibers. As the base contaminant and reagent react, the contaminant is retained within the longitudinal slots of the fiber.
In a preferred embodiment, the contaminants are ammonium and/or amines and the reagent is an acid. The acid-impregnated multilobal fiber is significantly more efficient than several commercially available filters. The filter can be used in a variety of applications including clean rooms and in filtering chambers for installation in the field.